Remove string from chicken, if present, and quarter chicken. Heat oil in 12-inch skillet over medium-high heat. Cook chicken quarters, skin side down, 3 to 4 minutes or until brown. Remove from skillet. Add squash, garlic, and 1/4 teaspoon each salt and pepper to drippings in skillet. Cook 2 minutes, stirring occasionally.
Return chicken to skillet, skin side up. Cook, covered, over medium heat about 10 minutes or until chicken is heated through and squash is tender, adding the tomatoes the last 2 minutes of cooking. Transfer chicken and squash mixture to platter and sprinkle with arugula. Makes 4 servings.